Question

Under isothermal conditions, a gas at $300\text{K}$ expands from $0.1\text{L}$ to $0.25\text{L}$ against a constant external pressure of $2\text{bar}$. The work done by the gas is:
[Given that $1\text{L .bar}=100\text{J}$]

• A. $25\text{J}$
• B. $30\text{J}$
• C. $-30\text{J}$
• D. $5\text{kJ}$

Answer 1

The correct option is B $30\text{J}$

Expansion of a gas against a constant external pressure is an irreversible process. The work done in an irreversible process

$W=-P_{ext}\Delta V=-P_{ext}(V_2-V_1)=-2(0.25-0.1)$
$W=-2\times 0.15\text{L-bar}=-0.30\times 100J=-30\text{J}$